Prevention of corrosion in steam generation



trines.

Patented Jan. 1, 1952 s 1 PREVENTION OF CORROSION IN STEAM GENERATIONArthur L. Jacoby, Western Springs, Ill., assignor to National AluminateCorporation, Chicago, 111., a corporation of Delaware No Drawing.Application June 19, 1947, Serial No. 755,739

This invention relates to the art of treating water in boilers, steamgenerators, evaporators and the like, and the treatment of the steam andthe condensate produced therefrom to reduce or prevent the corrosion ofsteam lines, traps, condensers and other pieces of equipment carryingthe steam and the condensate. The invention also relates to thepreparation of new and improved water treating compositions.

It has heretofore been suggested that certain amines may be added toboiler water from which they will volatilize with the steam and condenseand dissolve in the condensed steam to inhibit corrosion occurring inthe condensate lines. These amines may also be added directly to thesteam lines. The amines proposed for this purpose are liquids boilingwithin the range from degrees C. to 171 degrees C. at atmosphericpressure. These liquid amines are, in general. highly caustic andpresent a serious hazard in their handling. Furthermore, they are quitevolatile even under ordinary temperature conditions and the toxicity oftheir fumes in high concentrations presents a further hazard in theiruse. -Moreover, the addition of liquid to a boiler or to the steam linesis attended with many mechanical and practical difliculties.

One of the objects of the present invention is to provide a compositionfor the treatment of boiler water, steam and steam condensates, whichcomposition is in substantially dry form that is readily soluble ordispersible in water, and from which suitable amines are liberated bythe action of alkaline boiler water. v

Another object of the invention is to prepare corrosion inhibitingcompositions of the type described in the form of briquettes which aregradually and uniformly dissolved in the feed water to a steam boiler,evaporator or the like. Other objects will appear hereinafter.

r In accomplishing these objects in accordance with the invention it hasbeen found that corrosion inhibiting amines suitable for use in steamgenerating systems can be prepared in the form of crystallinenon-hygroscopic water soluble salts. These amine salts are solids whichare capable of liberating the free amines when added to the feed waterof a steam boiler containing suilicient alkali to decompose the aminesalts into free amines at steam generating temperatures. These solidamine salts can also be incorporated with other water treating chemicalseither by mixing them together to produce a dry, free flowing powder orby briquetting them with a suitable binder, preferably one which iswater soluble. The preferred compositions consist of the amine saltsbriquettedwith other water treating chemicals, e. g., tannins. ligninsulfonates, sodium sulfite, or the like, by means of binders such asdex- Claims. (Cl. 252--180)' Assuming that the alkali added to theboiler water' is sodium hydroxide, the general reaction which occursbetween the amine salt and the alkali with the liberatirn of the aminemay 'be described by the following equation:

Amine salt+NaOH (boiler water) Amine (volatile) +Na-salt (boiler water)Generally speaking, the quantities of amine salt required for thepurpose of the invention are so small that the quantities of alkaliemployed in the boiler water will be sufficientto react with the aminesalt and liberate the free amine while still maintaining an alkalinecondition in the boiler water. In some cases, however, where the aminesaltis made up with an'excess of acid or acid salt, it may be desirableto ,add larger amounts of alkali to the boiler feed water to compensatefor the alkali which is utilized inthe reaction with the amine salt. Thequantity of alkali required for this purpose can readily be calculatedby any one skilled in the art.

The amines which are useful for the prepara tion of amine salts inaccordance with the prac? tice of the invention are, in general,aliphatic,

alicyclic', cycloaliphatic, aromatic, and, heterofrom 5 to 250 poundsper square inch or at higher pressures if such pressures are employed, vH h 2. The amine should not cause foaming and carryover.

3. It should not decompose appreciably under boiler conditions ofalkalinity, pH, pressure and temperature. 4; The boiling point of theamine should preferably be above degreesC. so that appreciable. amountsof the amine are not lost in venting or preheating of the feed water andso most of the amine will be in the liquid phase in the portions of thesystem handling hot condensate. It should be pointed out thatboilingpoin't alone is not the factor which determines the relativevolatility of the amine with steam, as the. tendency to form stablehydrates and other factors also influence this behavior.

5. The amine should not form stable carbonic acid addition productswhich will not decompose to the amine and carbon dioxide at preheatertemperatures. v p

6. The carbonic acid addition products'of the amine should be reasonablywater soluble.

7. The amine should have a low' 'equivalent weight. The lower the weightof thegamine for each. neutralizing amino group the lessi'the 'quaninhibit corrosion in Specific examples of suitable amines for most steamsystems are: morpholine (B. P. 126-130 degrees C.) monoethanolamine (B.P. 171 degrees C.), cyclohexylamine (B. P. 134 degrees C), benzylamine(B. P. 184 degrees C.) and dimethylethanolamine (B. P. 133.5 degreesC.). These amines are miscible with water in all proportions. Otheramines, such as aniline, which is only partially soluble in water, areunsatisfactory for the purpose of the invention. Amines which aresoluble in water but have relatively high boiling points, e. g.,triethanolamine, which boils around 280 degrees C. under a partialvacuum are not adapted for steam generation under pressures within thepreferred range from to 250 pounds per square inch but might be used insteam generation under higher pressures and thecorrespondingtemperatures. It will be observed that the above describedamines are illustrative of primary, secondary and tertiary amines.

The amine salts of mineral acids and organic carboxylic and/or sulfonicacids can be prepared .by dissolving the acid in a solvent, e. .g.,water, diethyl ether or methanol, and adding the equivalent quantity ofamine with stirring at arate such as to avoid overheating. Cooling maybe resorted to in some cases. The salt is then recovered by filtrationand, if necessary, evaporation. In cases where the corresponding amideis water insoluble care must be taken in the preparation of the salt toavoid dehydration to the amide. Another way in which the amine salts maybe conveniently prepared consists in conducting the neutralization ofthe amine in the presence of a solid material capable of absorbing thewater of reaction,

thereby yielding a dry appearing product withare suitable for thepractice of the invention, for}. example, cyclohe'xylamine, sodiumsulfate (i. a, the sodium ammonium sulfate), the mixed morpholine saltsof lignin sulfonic acid and sulfuric acid, morpholine sodium sulfate. Inreacting the amines with the alkali metal acid salts, an excess of theacid salt was used and hence the amine groups were neutralized.

The above mentioned amine salts or mixed fame salts are substantiallynon-hygroscopic solid water soluble salts, but it will be understoodthat not all amine salts have satisfactory properties for the purpose ofthe invention even though. the amine itself may be suitable in otherrespects for inhibiting corrosion in a steam system. Thus, theorthophosphite, the metaphosphate, the arsenate, the bor-ate, thesulfite, the

benzene sulfonate and the paratoluene sulfonate .of morpholine were allfound to be too hygroscopic for the purpose of the invention. Similarly,the hydrochloride, the nitrate, the sulfate,

out the addition of anhydrous sodium sulfate.

The amine will then be converted to a mixed amine salt, namely, sodiumamine sulfate, and the water will be absorbed by the excess of salt orsalts producing a dry appearing powder.

The following amine salts or mixed salts have been prepared inaccordance with the invention and have been found to be suitable for thepractics of the invention:

A. The hydrochloride, the hydrobromide, the nitrate, the sulfate, theorthophosphate, the acetate, the phenyl acetate, and the '2-n-aphthalenesulfonate of morpholine;

. B. The hydrochloride, the hydrobromide, the nitrate, the sulfate, theorthophosphate, the acetate, the phenyl acetate, the pyrophosphate saltof cyclohexylamine and the 2-naphtha-lene sulfonate of cyclohexylamine;

C. The hydrochloride, the hydrobromide, the orthophosphate, the phenylacetate, the acid oxalate of monoethanolamine, and the 2-naphthalenesulfonate of vmonoethanolamine;

D. The nitrate, the sulfate, the orthophosphate, the acetate, the phenylacetate and the Z-napthalene sulfonateof henzylamine; and

E. The acid oxalate of dimethylethanolamine.

Additionally, mixed alkali metatamine salts the orthophosp'hate, theacetate, the phenyl acetate and the 2-napthalene sulfonate ofdimethylethanolamine were too hygroscopic to be isolated. The nitrate,the sulfate and the acetate of monoethanolamine were all toohygroscopic,

The following examples are given to show methods of preparing aminesalts suitable for the practice of the invention and also to illustratethe preparation of compositions containing such salts, it beingunderstood, however, that these examples are not intended to limit thescope of the invention.

Example I To 8? parts by weight of morpholine was added 85.? parts byweight of 70% nitric acid. The addition was made with thorough mixingand at a rate such that the temperature was maintained at degrees C. todegrees C. When the addition was complete the temperature was permittedto drop and the mixture became a heavy mass of damp crystals which wereuseful in that state if mixed with sufficient other water solubleportions of a water treating composition, or were readily dried to apoint where they were free flowing by themselves or compatible withother chemicals to give a powdered product containing a greater aminesalt content than would be possible in the compositions containing themoist salt.

Example II Morpholine sulfate was prepared in the manner described inExample I except that equivalent amounts of concentrated sulfuric acidwere employed instead of the nitric acid. It was found that by keepingthe temperature of neutralization at 50 C. or below, the amine salt wasmuch less prone to absorb moisture and gave a better product. Theresultant product was a white granular powder of very faint morpholineodor. Similarly, the hydrochloride, the orthophosphate and thehydrobromide of morpholine were prepared using the appropriate acidinstead of the nitric acid of Example I.

'In a like manner, by substituting equivalent amounts of the amineand/or the acid, the following amine salts were prepared; thenitrate,the sulfate and the orthophosphate of cyclohexylamine; the hydrochlorideand the orthophosphate of monoethanolamine; and the sulfate,

the nitrate and the orthophosphate of benzylamine to the solidcomponents, omitting the binder (dextrin) and water until last. Themix-i ing was conveniently done in a putty chaser.

The materials shown were made into briquettes;

Example III Parts Alkali soluble humic acids.- 10 Cyclohexylamine v 5-Sodium sulfate, anhydr 3.5- Ground nitre cake 4 Dextrin 2 Water 1Example IV 'Per cent Morpholine nitrate 65 Monosodium phosphate, anhydr12 Sodium acid pyrophosphate a. 15 Ammonium sulfate .5 Water (trace usedduring briquetting) Dextrin {3 Example V Per cent. Morpholine nitrate 66Ammonium sulfate ;5 Chestnut tannin, dry 13- Sodium sulfite 5- Dextrin 9Water (used in briquetting) 2 Example VI Per cent Morpholine nitrate .25Sodium sulfate 31 Sodium sulfite 31 Dextrin 8 Water -5 Example VII Therewas first prepared a mixture of morpholine salts of lignin sulfonic acidand sulfuric acid in the following manner. One part of morpholine and2.2 parts of lignin sulfonic'acid (obtained from waste sulfite liquors)were mixed and suflicient dilute sulfuric acid added to bring the pHdown to about 4.7. This material was then dried on a drum drier to amoisture con-. tent of about- 6% to 7%, whereupon it was found tube adry, water soluble powder. The amine As previously stated, in order tointroduce the {amine saltinto the steam system it is preferable -toprepare it in the form of a briquette with other 'water treatingchemicals and to cause it .-to be dissolved uniformly and gradually by:the -feed water-to the boiler. This is conveniently accomplished bypreparing the .briquette and intro'ducing it into 'a by-pass feederwhich isconf- -nected in the boiler feed water line. The boiler feedwater circulates through the feeder, grad: ually dissolving thebriquette and carrying the amine salt into the boiler where the amine isliberated by the action of the heat and inorganic alkali present. Theliberated amine is then "in suflicient amount-to produce a pH preferablyvolatilized at a uniform rate' such that little change occurs in thewater 'to amine ratio. The manner in which the aminevolatilizes will, ofcourse, depend upon the chemical and physical characteristics of theamine. The volatilized amine should serve to provide a. nearly constantalkalinity in the boiling water and should redissolve in the steamcondensate to provide the desired alkalinity in the latter at the pointwhere condensation occurs.

The quantity of the amine salt initially added to the water from whichthe steam is generated should preferably be approximately 0.015 poundfor each neutralizing amino group per grain of methyl orange alkalinityper thousand gallons of water. This means that if the methyl orangealkalinity of the feed water were 10 the quantity of amine salt would bethat quantity'capable of liberating 0.15 pound of said amine perthousand gallons of feed water. If the methyl orange alkalinity were 20the recommended dosage of amine salt would be the equivalent of 0.30pound of said amine per thousand gallons of water. In a similar mannerthe dosage can be calculated for waters of different alkalinities. Thesedosages are based upon a pressure of 250 p. s. i. and the correspondingsteam temperatures with adequate venting of the preheater.

The dosage can also be established by observation of the pH obtained inthe condensate. In general, it is preferable to maintain a pH in thesteamcondensate of about 7.0, although ithas been observed thatsubstantial corrosionprotection has been obtained at a lower pH, as lowas o 6.3. The preferred pH range in the steam condensate is about 6.5 toabout 7.5.

' The treatment described herein can be employed in steam generationwhere the steam generators are operated at operating pressures from ahigh vacuum to rather high super-atmospheric pressures. It will beunderstood, however, that of the amines suggested some would be betterthan others for different pressure operations. Thus, for treatmentsinvolving vacuum evaporation the amine salts of cyclohexylamine' arerecommended. For corrosion prevention or inhibition in steam generatingsystems "operating at superatrncspheric pressures within the range of to250 pounds per squareinch and the cor.-

responding temperatures degrees C. to 210 degrees C.) excellent'resultshave been obtained with the amine salts of morpholine. Having thusdescribed the invention, what I claim as new and desire to secure byLetters Patent of the United States is:

1. In a system wherein steam is generated from a boiler 'watercontaining an alkali and condensed, the process which comprisesintroduc- 'ing into said 'boiler'water-containing an alkali a quantity'of' a substantially non-hygroscopic water'soluble salt of a mono-aminemiscible with water in all proportions and volatile with steam at theboiler temperatures and pressures, the .quantity of alkali in saidboiler water being in excess of the amount required to hydrolyze saidamine salt to the free amine, and the quantity of. amine saltbeing'efiective to liberate. a corros'ion' inhibiting quantity" of saidvolatile amine in the steam condensate of at least 6.3. f

- 2. In a system wherein steam -isgenerated -irom a boiler watercontaining an alkali and condensed, the process which comprisesintroducing into said boiler water containing an ,alkali: a quantity of,a substantially nonz -hy rosoopic water soluble salt of a mono-aminemiscible with water in all proportions and volatile with steam at theboiler temperatures and pressures, the quantity of alkali in said boilerwater being in excess of the amount required to hydrolyze said aminesalt to the free amine, and the quantity of amine salt being efiectiveto liberate a corrosion inhibiting quantity of said volatile amine insufiicient amount to produce a pH in the steam condensate within therange of about 6.5 to about 7.5.

3. In a system wherein steam is generated from a boiler water containingan alkali and condensed, the process which comprises introducing intosaid boiler water containing an alkali a quantity of a substantiallynon-hygroscopic water soluble salt of a mono-amine miscible with waterin all proportions and volatile with steam at the boiler temperaturesand pressures, the quantity of alkali in said boiler water being inexcess of the amount required to hydrolyze said amine salt to the freeamine, and the quantity of amine salt corresponding to that quantitycapable of liberating approximately 0.015 pound of amine per grain ofmethyl orange alkalinity per thousand gallons of boiler feed water.

4. In a system wherein steam is generated and condensed the method ofprotecting metal parts of the system against corrosion which comprisesincorporating into boiler feed water, from which the steam is generated,and which contains an alkali, a quantity of a substantiallynon-hygroscopio morpholine salt, the quantity of alkali in saidboilerwater being in excess of the amount required to hydrolyze saidmorpholine salt to free morpholine, and the quantity of morpholine saltbeing effective to liberate a corrosion inhibiting quantity ofmorpholine in sufiicient amount to produce a pH in the steam condensateof at least 6.3. Y

5. In a process of generating steam the method which comprisesgenerating steam from an alkaline boiler water at pressures within therange of 100-250 pounds per square inch and the correspondingtemperatures while incorporating into the feed water to the boiler aquantity of nonhygroscopic water soluble salt of morpholine, thequantity of alkali in the alkaline boiler water being in excess of theamount required to hydrolyze said morpholine salt and the quantity ofthe morpholine salt being sufficient to liberate a corrosion inhibitingquantity of morpholine upon said hydrolysis in suflicient amount toproduce a pH in the steam condensate of at least 6.3.

6. In a process of generating steam the method which comprisesgenerating steam from an alkaline boiler water at a pressureapproximating 250 pounds per square inch, and the correspondingtemperature while incorporating with the boiler feed water a quantity ofa water soluble substantially non-hygroscopic morpholine salt capable ofliberating approximately 0.015 pound of morpholine per grain of methylorange alkalinity per thousand gallons of boiler feed water, thequantity of alkali in said boiler water being in excess of the amountrequired to hydrolyze said morpholine salt, and the quantity ofmorpholine salt being suflicient to maintain a pH in the steamcondensate within the range of about 6.5 to 7.5.

'7. In a process or generating steam the method which comprisesgenerating steam from an alkaline boiler water at pressures within therange of 100 to 250 pounds per square inch, and the correspondingtemperatures, while incorporating into the boiler feed water a quantityof morpholine nitrate, the quantity of alkali in in the alkaline boilerwater being in excess of the amount required to hydrolyze saidmorpholine nitrate, and the quantity of morpholine nitrate beingeffective to liberate a quantity of morpholine sufficient to produce apI-I in. the steam condensate within the range of 6.5 to 7.5.

8. In a process of generating steam the method which comprisesgenerating steam from an alkaline boiler water at pressures within therange of to 250 pounds per square inch, and the correspondingtemperatures, while incorporating into the boiler feed water a quantityof morpholine sulfate, the quantity of alkali in the alkaline boilerwater being in excess of the amount required to hydrolyze saidmorpholine sulfate, and the quantity of morpholine sulfate beingeffective to liberate a quantity of morpholine sufficient to produce apH in the steam condensate within the range of 5.5 to 7.5.

9. In a process of generating steam the method which comprisesgenerating steam from an alkaline boiler water at pressures within therange of 100 to 250 pounds per square inch, and the correspondingtemperatures, while incorporating into the boiler feed water a quantityof cyclohexylamine sulfate, the quantity of alkali in the alkalineboiler water being in excess of the amount required to hydrolyze saidcyclohexylamine sulfate, and the quantity of cyclohexylamine sulfatebeing effective to liberate a quantity of cyclohexylamine sufiicient toproduce a pH in the steam condensate within the range of 6.5 to 7.5.

10. In the process of generating steam the method which comprisesgenerating steam from an alkaline boiler water at pressures within therange of 100 to 250 pounds per square inch, and the correspondingtemperatures, while incorporating into the boiler feed water a quantityof a mixed aminesalt oi morpholine lignin sulfonate and morpholinesulfate, the quantity of alkali in the alkaline boiler water being inexcess of the amount required to hydrolyze said mixed amine salt ofmorpholine lignin sulfonate and morpholine sulfate, and the quantity ofmixed amine salt of morpholine lignin sulfonate and morpholine sulfatebeing effective to liberate a quantity of morpholine suilicient toproduce a pH in the steam condensate within the range of 6.5 to 7.5.

ARTHUR L. JACOBY.

REFERENCES CITED The following references are of record in the file ofthis patent:

OTHER REFERENCES Dictionary of Organic Compounds; Heilbron,

OxfordPress, N. Y., vol. 2 (19 3), p. 840.

1. IN A SYSTEM WHEREIN STEAM IS GENERAGED FROM A BOILER WATER CONTAININGAN ALKALI AND CONDENSED, THE PROCESS WHICH COMPRISES INTRODUCING INTOSAID BOILER WATER CONTAINING AN ALKALI A QUANTITY OF A SUBSTANTIALLYNON-HYGROSCOPIC WATER SOLUBLE SALT OF A MONO-AMINE MISCIBLE WITH WATERIN ALL PROPORTIONS AND VOLATILE WITH STEAM AT THE BOILER TEMPERATURESAND PRESSURES, THE QUANTITY OF ALKALI IN SAID BOILER WATER BEING INEXCESS OF THE AMOUNT REQUIRED TO HYDROLYZE SAID AMINE SALT TO THE FREEAMINE, AND THE QUANTITY OF AMINE SALT BEING EFFECTIVE TO LIBERATE ACORROSION INHIBITING QUANTITY OF SAID VOLATILE AMINE IN SUFFICIENTAMOUNT TO PRODUCE A PH IN THE STEAM CONDENSATE OF AT LEAST 6.3.